Warn when project-specific settings are passed to non-project `uv run` commands (#5977)

## Summary

Closes https://github.com/astral-sh/uv/issues/5856.

crates/uv/src/commands/project/init.rs

@@ -167,10 +167,7 @@ async fn init_project(
     printer: Printer,
 ) -> Result<()> {
     // Discover the current workspace, if it exists.
-    let workspace = if no_workspace {
-        None
-    } else {
-        // Attempt to find a workspace root.
+    let workspace = {
         let parent = path.parent().expect("Project path has no parent");
         match Workspace::discover(
             parent,
@@ -188,6 +185,17 @@ async fn init_project(
         }
     };
 
+    // Ignore the current workspace, if `--no-workspace` was provided.
+    let workspace = if no_workspace {
+        // If the user runs with `--no-workspace` and we can't find a workspace, warn.
+        if workspace.is_none() {
+            warn_user_once!("`--no-workspace` was provided, but no workspace was found");
+        }
+        None
+    } else {
+        workspace
+    };
+
     // Add a `requires-python` field to the `pyproject.toml`.
     let requires_python = if let Some(request) = python.as_deref() {
         // (1) Explicit request from user

crates/uv/src/commands/project/run.rs

@@ -187,11 +187,42 @@ pub(crate) async fn run(
     // Discover and sync the base environment.
     let temp_dir;
     let base_interpreter = if let Some(script_interpreter) = script_interpreter {
+        // If we found a PEP 723 script and the user provided a project-only setting, warn.
+        if !extras.is_empty() {
+            warn_user_once!("Extras are not supported for Python scripts with inline metadata");
+        }
+        if !dev {
+            warn_user_once!("`--no-dev` is not supported for Python scripts with inline metadata");
+        }
+        if no_project {
+            warn_user_once!(
+                "`--no-project` is a no-op for Python scripts with inline metadata, which always run in isolation"
+            );
+        }
+        if package.is_some() {
+            warn_user_once!(
+                "`--package` is a no-op for Python scripts with inline metadata, which always run in isolation"
+            );
+        }
+        if locked {
+            warn_user_once!(
+                "`--locked` is a no-op for Python scripts with inline metadata, which always run in isolation"
+            );
+        }
+        if frozen {
+            warn_user_once!(
+                "`--frozen` is a no-op for Python scripts with inline metadata, which always run in isolation"
+            );
+        }
+        if isolated {
+            warn_user_once!(
+                "`--isolated` is a no-op for Python scripts with inline metadata, which always run in isolation"
+            );
+        }
+
         script_interpreter
     } else {
-        let project = if no_project {
-            None
-        } else if let Some(package) = package {
+        let project = if let Some(package) = package {
             // We need a workspace, but we don't need to have a current package, we can be e.g. in
             // the root of a virtual workspace and then switch into the selected package.
             Some(VirtualProject::Project(
@@ -209,6 +240,47 @@ pub(crate) async fn run(
             }
         };
 
+        let project = if no_project {
+            // If the user runs with `--no-project` and we can't find a project, warn.
+            if project.is_none() {
+                warn_user_once!("`--no-project` was provided, but no project was found");
+            }
+
+            // If the user ran with `--no-project` and provided a project-only setting, warn.
+            if !extras.is_empty() {
+                warn_user_once!("Extras have no effect when used alongside `--no-project`");
+            }
+            if !dev {
+                warn_user_once!("`--no-dev` has no effect when used alongside `--no-project`");
+            }
+            if locked {
+                warn_user_once!("`--locked` has no effect when used alongside `--no-project`");
+            }
+            if frozen {
+                warn_user_once!("`--frozen` has no effect when used alongside `--no-project`");
+            }
+
+            None
+        } else {
+            // If we can't find a project and the user provided a project-only setting, warn.
+            if project.is_none() {
+                if !extras.is_empty() {
+                    warn_user_once!("Extras have no effect when used outside of a project");
+                }
+                if !dev {
+                    warn_user_once!("`--no-dev` has no effect when used outside of a project");
+                }
+                if locked {
+                    warn_user_once!("`--locked` has no effect when used outside of a project");
+                }
+                if frozen {
+                    warn_user_once!("`--frozen` has no effect when used outside of a project");
+                }
+            }
+
+            project
+        };
+
         let interpreter = if let Some(project) = project {
             if let Some(project_name) = project.project_name() {
                 debug!(

crates/uv/tests/init.rs

@@ -704,6 +704,47 @@ fn init_no_workspace() -> Result<()> {
     Ok(())
 }
 
+/// Warn if the user provides `--no-workspace` outside of a workspace.
+#[test]
+fn init_no_workspace_warning() -> Result<()> {
+    let context = TestContext::new("3.12");
+
+    uv_snapshot!(context.filters(), context.init().current_dir(&context.temp_dir).arg("--no-workspace").arg("--name").arg("project"), @r###"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+
+    ----- stderr -----
+    warning: `uv init` is experimental and may change without warning
+    warning: `--no-workspace` was provided, but no workspace was found
+    Initialized project `project`
+    "###);
+
+    let workspace = fs_err::read_to_string(context.temp_dir.join("pyproject.toml"))?;
+
+    insta::with_settings!({
+        filters => context.filters(),
+    }, {
+        assert_snapshot!(
+            workspace, @r###"
+        [project]
+        name = "project"
+        version = "0.1.0"
+        description = "Add your description here"
+        readme = "README.md"
+        requires-python = ">=3.12"
+        dependencies = []
+
+        [build-system]
+        requires = ["hatchling"]
+        build-backend = "hatchling.build"
+        "###
+        );
+    });
+
+    Ok(())
+}
+
 #[test]
 fn init_project_inside_project() -> Result<()> {
     let context = TestContext::new("3.12");

crates/uv/tests/run.rs

@@ -320,6 +320,18 @@ fn run_pep723_script() -> Result<()> {
     Reading inline script metadata from: main.py
     "###);
 
+    // Running a script with `--no-project` should warn.
+    uv_snapshot!(context.filters(), context.run().arg("--preview").arg("--no-project").arg("main.py"), @r###"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+    Hello, world!
+
+    ----- stderr -----
+    Reading inline script metadata from: main.py
+    warning: `--no-project` is a no-op for Python scripts with inline metadata, which always run in isolation
+    "###);
+
     Ok(())
 }
 
@@ -1119,5 +1131,29 @@ fn run_no_project() -> Result<()> {
     warning: `uv run` is experimental and may change without warning
     "###);
 
+    // `run --no-project` should not (but it should still run in the same environment, as it would
+    // if there were no project at all).
+    uv_snapshot!(context.filters(), context.run().arg("--no-project").arg("python").arg("-c").arg("import sys; print(sys.executable)"), @r###"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+    [VENV]/[BIN]/python
+
+    ----- stderr -----
+    warning: `uv run` is experimental and may change without warning
+    "###);
+
+    // `run --no-project --locked` should fail.
+    uv_snapshot!(context.filters(), context.run().arg("--no-project").arg("--locked").arg("python").arg("-c").arg("import sys; print(sys.executable)"), @r###"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+    [VENV]/[BIN]/python
+
+    ----- stderr -----
+    warning: `uv run` is experimental and may change without warning
+    warning: `--locked` has no effect when used alongside `--no-project`
+    "###);
+
     Ok(())
 }